1. Field of the Invention
The present invention relates to a polymer preparing method and a polymer prepared by the same.
2. Discussion of Related Art
Hydrophobic polymers such as fluorine-containing polymers or olefin-based polymers have been applied to various fields such as membranes, filters, binder polymers for batteries, pipe products, and optical films for a display due to their excellent chemical, mechanical, and thermal stabilities. However, when these hydrophobic polymers are applied to such fields, it is not easy to control hydrophobic levels of the polymers. As for a linear polymer, applicable processes are limited due to its structural property. Thus, there have been carried out researches on modification of chemical and structural properties of polymers, such as researches on graft polymerization for introducing a hydrophilic monomer to a side chain of a hydrophobic linear polymer.
For example, as an attempt to introduce a monomer to a side chain of a linear polymer, that is, as graft polymerization, graft-from polymerization in which a hydrophobic polymer contains a halogen activating group such as chlorine and various monomers are polymerized by using the activated group is known to be efficient.
Specifically, in the graft-from polymerization, when a halogen activating group such as chlorine leaves, radicals are generated. As a catalyst for bonding the halogen to an activating group, a metal/ligand complex compound may be used. As suitable metal/ligand complex compounds, complex compounds of, for example, Cu, Ru, Fe, Ni, Zn, and the like may be used. As the copper/ligand complex compound most widely used among them, a copper/ligand complex compound can be used. It is known that when the copper/ligand complex compound is bound to the halogen activating group, its activated form is known as Cu(I)X/L (X represents a halide and L represents a ligand).
Atom Transfer Radical Polymerization (hereinafter, referred to as “ATRP”) is known as polymerization using the Cu(I)X/L as a catalyst. However, in the case of polymerization, according to the ATRP, when a chlorine group in a hydrophobic polymer is activated by using an ATRP mechanism, a great amount of the Cu(I)X/L needs to be used due to low reaction initiation efficiency, and thus, it may be difficult to remove a catalyst compound after the reaction. In order to adjust a length of a polymer chain grafted by using the ATRP, initiation efficiency of a halogen site in a halogenated hydrophobic polymer may be adjusted. In this case, by reducing an amount of the metal catalyst used to slow down an initiation rate, initiation efficiency can be low and a long polymer chain can be formed. However, according to the ATRP, when an amount of the catalyst is small, an inactivation reaction mainly occurs. Thus, an initiation rate is remarkably reduced and an initiation reaction may not occur or may occur at a very low reaction rate. Further, after the initiation, the polymer chain may be grown at a very low growth rate, so that the polymerization may be ended with a low conversion ratio. On the contrary, when an amount of the catalyst used is increased, an initiation reaction occurs at too many sites in the halogenated hydrophobic polymer, so that the polymer chain generates heat and gelates due to a coupling phenomenon of the halogenated hydrophobic polymer, and thus, the polymer chain cannot be grown.
Therefore, there has been suggested an Activators Regenerated by Electron Transfer-ATRP (hereinafter, referred to as “ARGET-ATRP”) in which Cu(II)X2 is used as a catalyst instead of the Cu(I)X/L and a catalytic reducing agent is input together in the initial stages or Single Electron Transfer-Living Radical Polymerization (hereinafter, referred to as “SET-LRP”) in which Cu(0) is used as both a catalyst and a catalytic reducing agent.
FIG. 1 is a schematic diagram of a suggested mechanism of the SET-LRP.
As shown in FIG. 1, an initiation step (kact) is mediated by a single electron transfer from an electron donor that donates electrons to an electron acceptor (halogenated polymer compound, Pn—X) that accepts electrons. The electron donor may be, for example, Cu(0). The Cu(0) is known as an effective single electron donor. Cu(I) species generated during the initiation step can be disproportionated immediately and spontaneously into Cu(II) and Cu(0) species. The Cu(II) species generated from the disproportionation reaction as an inactivated catalyst with extremely high reactivity offers reversible inactivation (kdeact) to potentially alkyl halide species (Pn—X) of generated radicals (Pn.) and are reduced to the Cu(I) species as an activated catalyst. During reaction conditions that favor the disproportionation of the Cu(I) species into the Cu(II) species and Cu(0) species, the lifetime of Cu(I)X is very short in comparison with those of Cu(II)X2 and Cu(0). Therefore, SET catalytic activity of Cu(I)X may be neglected (X represents a halogen element).
When an activation rate constant of the alkyl halide species (Pn—X) is high, it may be difficult to control a polymerization rate. Thus, in order to control an initiation reaction, even a small amount of the Cu(II) species as an inactivated catalyst species may be input together.
In the case of polymerization using the SET-LRP, initiation efficiency is low in comparison with growth efficiency of a chain. Therefore, an initiation reaction of a halogenated hydrophobic polymer proceeds relatively slowly as compared with the ATRP, and thus, a relatively long polymer chain may be formed. Further, a polymerization rate is also high as compared with the ATRP, and thus, a polymer having a high conversion ratio may be prepared.
FIG. 2 is a graph illustrating changes in polymerization rate and molecular weight based on comparison between polymerization using the SET-LRP and polymerization using the ARGET-ATRP.
Referring to FIG. 2, in the case of the polymerization using the SET-LRP, even though a very small amount of a catalyst is used as compared with the polymerization using the ARGET-ATRP, a reaction may be initiated with efficiency, and thus, it is easy to remove the catalyst after the reaction. Further, the SET-LRP may be carried out with lower activation energy at a lower temperature and may have higher overall polymerization efficiency as compared with the polymerization using the ARGET-ATRP.
However, in the case of graft polymerization using the SET-LRP, a growth reaction (kact) of a polymer actively occurs, so that a concentration of radicals generated is increased. Thus, a reaction rate of a stop reaction (kt) is remarkably increased and the Cu(II) species as an inactivated catalyst species are accumulated. Therefore, the polymerization may be ended at a low conversion ratio of a monomer to be polymerized.